The invention relates to a pressure gauge, more particularly to a compact pressure gauge which is easily manufactured and adjusted.
To achieve a convenient reading when measuring the air pressure in a horizontal tube, I disclosed, in my U.S. Pat. No. 4,785,670, a pressure gauge as shown in FIG. 1 which has a body A, an adapter B with a horizontal intake passage B1, and an outer housing C with a central hole C1. The body A has a central bore E which is sealed by engaging threadably the upper end of the body A with an externally threaded cap A1. To intercommunicate the intake passage B1 of the adapter B and the central bore E of the body A, the body A is drilled to form gas passages E1, E2. The upper end of the passage E1 is sealed by engaging threadably the body A with a bolt A2. The formation of the passages E1, E2 increases the volume of the pressure gauge and makes the manufacture of said pressure gauge more difficult and time-consuming. To reduce the volume of the pressure gauge, I disclosed, in my U.S. Pat. No. 4,742,714, a compact pressure gauge as shown in FIG. 2, which is characterized by a U-shaped piston rod F. As illustrated, the compact pressure gauge includes an abutment element H which is engaged threadably with the left arm of the piston rod F. Although the pressure gauge of FIG. 2 has a smaller volume, it is difficult to adjust the biasing force of a spring G. In particular, to adjust the biasing force of the spring G, several parts must be removed from the pressure gauge so as to rotate the abutment element H relative to the piston rod F by engaging the screwdriver hole of the upper end surface of the abutment element H with the head of a screwdriver.